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A selection can result in a statement being executed once or not at all. What determines whether the statement will be executed or not is the result of a test If the result of the test is true then the statement will be executed, if the result is false it will not be executed. There are three forms of selection statement implemented in Java:
In this module we shall concentrate on the first two of these selection statements. They are all technically equivalent; the choice as to which form of selection statement to implement in a program is made by each programmer on the grounds of style or convenience. In this unit we shall examine just the first (simpler) if selection statement. In the next unit we will examine the extended if...else selection statement and an iteration statement Selection: `if' Using pseudocode code we can illustrate how an if statement works. Consider the following pseudocode for a system to operate fire alarms in an office building:
This illustrates the general form of an if statement, i.e.:
To implement our fire alarm pseudocode as a valid Java statement we could write the following:
(of course we are assuming the class has a variable called temperature and a method soundAlarm()) The way an if statement can cause deviation from the default sequential flow of execution can be illustrated as follows. Consider this pseudocode design:
If the variable age has a value over 60, say 65, then the test ( age > 60 ) will be true, and the therefore statementB will be executed. So the statements to be executed will be:
However, if the variable age has a value of 60 or less, say 21, then the test ( age > 60 ) will be false, and statementB will not be executed. So the statements executed will be:
Thus the result of a selection statement means that some statements may not be executed, or may be executed once.
RITSEC - Global Campus |
